The present invention relates generally to systems and methods for harvesting energy contained in the off gases resulting from a direct iron making process or smelter. More particularly, the present invention relates to systems and methods of generating electricity using the off gases of the direct iron making process.
Various environmental and economic pressures are currently being exerted upon the iron and steel making industry to develop a direct iron making process that utilizes coal and other fuels, instead of coke, for the conversion of iron ores to liquid iron. Various direct iron making processes are known to those skilled in the art, and several are currently being developed and commercialized in various countries, such as the Australian HIsmelt and Ausi-Melt, the Dutch Cyclonic Converter Furnace, the Italian CleanSmelt, the Russian Romelt, and the United States A.I.S.I. process.
Several of the above-recited processes have been successful in producing iron and other hot metals by using coal rather than coke. However, most of the processes are very inefficient, because they produce large quantities of high temperature off gases that contain as much as 50% of the charged fuel energy.
Additionally, most of the known direct iron making processes require careful control of the pressure range at which the conversion from ore to liquid metal is carried out. Such pressures are generally above atmospheric pressure, and therefore, require additional pressure creating and controlling equipment. As such, methods of increasing the efficiency and economy of direct iron making processes are continually being sought.
Accordingly, the present invention provides a method of harvesting energy contained in off gases resulting from a direct iron making process or smelter which harvests the heat, pressure, and chemical energy of the off gases. The process includes the steps of: a) transferring heat energy from the direct iron making off gases to water, such that the water becomes steam and turns a steam turbine coupled to a power generator that produces electricity; b) transferring pressure energy from the direct iron making off gases to a power recovery expander coupled to a power generator, such that the generator produces electricity; and c) transferring chemical energy from the direct iron making off gases to water by combusting the off gases, such that the water heats to steam, and turns a steam turbine coupled to a power generator that produces electricity. In one aspect, the step of transferring heat energy to the water includes transferring a sufficient amount of heat energy to superheat the water.
In another aspect, the present method may further include the steps of: a) converting the superheated water to saturated steam; b) super heating the saturated steam in the super heater; and c) turning a steam turbine connected to a power generator with the super heated steam to generate electricity.
In yet another aspect, the step of super heating further includes transferring chemical energy from the off gases to the saturated steam in the form of heat by combusting the off gases.
In addition to the above recited aspects, the present method may include removing particulate matter from the off gas prior to the step of transferring pressure energy. In one aspect, the particulate matter may be removed using a cyclone dust extractor. In another aspect, an electrostatic precipitator may be used. Additionally, other forms of conventional particulate or dust removal equipment may be used.
The present method may also include the step of scrubbing the off gases following the combustion step to remove sulfur. In one aspect, the scrubbing may be a wet scrubbing. In another aspect, the scrubbing may be a dry scrubbing.
In addition to a method for harvesting energy from off gases, the present invention encompasses a system for performing such a process. In one aspect, such a system may include: a) a steam hood, operatively coupled to a direct iron making smelter, configured to transfer heat energy from the off gases into water and create steam; b) a steam turbine, operatively coupled to the steam hood and to a power generator, configured to receive steam from the steam hood, and generate electricity with the power generator; c) a power recovery expander, operatively coupled to the steam hood and to a power generator, configured to receive the off gases from the steam hood to condition the gases by means of conventional cooling system, if required, and to transfer pressure energy from the off gases to the power generator and generate electricity; d) a boiler unit, operatively coupled to the power recovery expander, configured to receive the low pressure off gases from the power recovery expander, and to transfer chemical energy from the off gases to water in the boiler unit in the form of heat, by combusting the off gases; and e) a steam turbine and power generator, coupled to the boiler unit, configured to receive steam from the boiler unit and generate electricity with the power generator.
In another aspect, the system may additionally include a steam drum, operatively coupled between the steam hood and the steam turbine, configured to convert high temperature high pressure water from the steam hood into saturated steam, and a super heater, operatively coupled between the steam drum, and the steam turbine, configured to super heat and unsaturated the steam.
In addition to the above recited elements, the system of the present invention may additionally include a particulate removal unit, operatively coupled between the steam hood, and the power recovery expander, configured to remove particulates from the off gases. In one aspect, the particulate removal unit may be a cyclone or conventional dust extractor. In another aspect, the particulate removal system may be an electrostatic precipitator.
While the power recovery expander is operatively coupled to the boiler unit, it may also be operatively coupled to the super heater, such that a portion of the off gases is directed to the super heater and combusted. As such, the off gases provide a source of fuel for conditioning the saturated steam to become suitable for use in a steam turbine.
The system of the present invention may also include a scrubbing unit, operatively coupled to the boiler unit, configured for scrubbing sulfur from the off gases received from the boiler unit. In one aspect, the scrubbing unit may be a wet scrubber. In another aspect, the scrubbing unit may be a dry scrubber.
There has thus been outlined, rather broadly, various features of the invention so that the detailed description thereof that follows may be better understood, and so that the present contribution to the art may be better appreciated. Other features of the present invention will become clearer from the following detailed description of the invention, taken with the accompanying claims, or may be learned by the practice of the invention.